after clyde craft insulted the boss for killing him (something like "screw you boss", I muted him for 50 seconds. After his mute ended, he said "yeah screw you too ike".
I muted him a second time after warning him, and he continued on with his behavior. After a bit, I kicked him after a warning and he came back and this happened.

I permanently banned him. I don't think he should be allowed at the server anymore. His behavior proves that he doesn't deserve to play a game that he can't keep decent while playing.
Also, I told him that if he wants to appeal the ban and be mature about it, he can do so in this thread.
(sorry for resizing it, photo bucket is gay and made the initial image smaller)